It is common for owners to equip commercial vehicles such as jeeps, 4.times.4's and pick-up trucks with snowplows. Each type of vehicle has a different frame structure and a different bumper to frame relationship. The vehicle must be provided with a plow blade unit support structure which is typically mounted to the frame of the vehicle. The plow blade unit support structure is known as a lift mount assembly. The lift mount assembly serves primarily to raise, lower and support the plow blade, such as by raising the blade above ground during transportation of the snowplow as well as during a snowplow operation, such as when the vehicle is moving backwards. The snowplow is removed for the summer but the frame mount typically stays permanently attached to the vehicle.
Depending on the type of frame mount used, the mount projects out beyond or coplanar with the bumper, thereby defeating the purpose of the bumper. The frame mount becomes a potentially dangerous battering ram when it extends past the bumper and is also subject to being damaged itself due to collision. This can be seen in prior art lift mount assemblies such as those disclosed in Swiss Patent No. 264,534 and U.S. Pat. Nos. 2,667,708 to Gjesdahl; 3,214,138 to Jocher et al; 3,410,008 to Standfuss; 3,456,369 to Leposky; and, 3,987,562 to Dean et al. Additionally, these prior art mount assemblies include one or more of a number of structural characteristics which are disadvantageous i) from the standpoint of weight, ii) exposure to adverse environmental conditions, iii) potential physical damage during non-snowplow use; and iv) cost of manufacture of the lift mount assembly and/or modification of the front of the vehicle to facilitate the attachment of the assembly thereto.
Assignee's U.S. Pat. No. 4,279,084 to Low et al improved on a number of the drawbacks of prior art lift mount assemblies which required modification of the front end of the vehicles to accommodate a lift mount assembly. Low replaced projecting parts of the lift mount assembly with somewhat recessed exposed parts which would not bear the full impact of a collision should the vehicle impact against an object during non-snowplow use.
However, the forwardmost part of the bracket portion of Low's lift mount assembly is located on the same vertical plane as the forwardmost part of the bumper. Therefore, both the bumper and the lift mount bear the brunt of any collision. The battering ram effect is thereby lessened but still exists in Low. Potential damage to the lift mount assembly remains a likelihood on collision. A second problem is that the Low lift mount assembly must be strung up behind the bumper, presenting installation problems. More specifically, the support unit carries a cylinder for raising and lowering the blade. To firmly anchor the lift arm cylinder prior art devices, including Low, require that the support unit be secured to the vehicle frame not only at the bottom, which corresponds to the lower part of the cylinder, but also at the top of the cylinder so that the cylinder is firmly mounted between two vertically spaced points which in turn are firmly fixed, vis-a-vis the frame housing unit to the frame. Since different vehicles have different bumper to frame relationships, Low does require some type of rigging to establish the top mounting point behind the bumper which is troublesome. This problem will be further aggravated should safety regulations be amended to require that bumpers on such vehicles absorb certain speed rated impacts. Such regulation would require the bumper to move relatively toward the frame mounted rigging which could prevent such movement. There is a strong likelihood of damage to the lift mount assembly if the bumper is pushed-in on collision. A third problem is that the exposed parts of Low are exposed to environmental conditions including salt erosion.